Support monies collected are assumed to be used for the child's expenses, including food, clothing, and ordinary educational needs. They are not meant to be used as "spending money" for the child or the parent. Courts might have held that it is unacceptable for child support payments to be used to directly benefit the custodial parent however such rulings are rare and difficult to prove or enforce.This might be wishful thinking. It is not the law in the USA. (I will edit this if no one else does, so it may read something else when you read this.)
In the USA, most child support orders are based on formulas of past income, and are unrelated to child expenses. The recipient is not required to spend the money on the child.
Here is Calif FC 4053:
(f) Children should share in the standard of living of both parents. Child support may therefore appropriately improve the standard of living of the custodial household to improve the lives of the children.So if the ex-husband wins the lottery and buys himself a Rolls Royce car, then the ex-wife can demand an increase in child support and spend all the money on a Rolls Royce for herself. Even if the ex-husband puts all the lottery winnings in the bank for his retirement, the ex-wife gets a percentage that she may spend on herself as she pleases.
(g) Child support orders in cases in which both parents have high levels of responsibility for the children should reflect the increased costs of raising the children in two homes and should minimize significant disparities in the children's living standards in the two homes.
And the more she withholds visitation and custody to the dad, the greater percentage she gets.
The whole child support system is destructive, and ought to be abolished. It sends good men to jail, it fuels custody fights and false accusations, it creates horrible disincentives against marriage and children, and the money is not even spent on the kids.